Classifications

• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04W—WIRELESS COMMUNICATION NETWORKS
  • H04W36/00—Hand-off or reselection arrangements
  • H04W36/16—Performing reselection for specific purposes
  • H04W36/18—Performing reselection for specific purposes for allowing seamless reselection, e.g. soft reselection
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04W—WIRELESS COMMUNICATION NETWORKS
  • H04W36/00—Hand-off or reselection arrangements
  • H04W36/24—Reselection being triggered by specific parameters
  • H04W36/30—Reselection being triggered by specific parameters by measured or perceived connection quality data
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04W—WIRELESS COMMUNICATION NETWORKS
  • H04W24/00—Supervisory, monitoring or testing arrangements
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04W—WIRELESS COMMUNICATION NETWORKS
  • H04W36/00—Hand-off or reselection arrangements
  • H04W36/02—Buffering or recovering information during reselection ; Modification of the traffic flow during hand-off
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04W—WIRELESS COMMUNICATION NETWORKS
  • H04W36/00—Hand-off or reselection arrangements
  • H04W36/24—Reselection being triggered by specific parameters
  • H04W36/30—Reselection being triggered by specific parameters by measured or perceived connection quality data
  • H04W36/304—Reselection being triggered by specific parameters by measured or perceived connection quality data due to measured or perceived resources with higher communication quality

Definitions

• the present invention relates generally to wireless communications, and more specifically to inter-frequency hard handoff of a wireless access terminal.
• Wireless communication systems have evolved from the first voice-only cellular telephone systems to high-speed digital data networks capable of delivering voice, Internet, and even streaming video content to miniature handheld units, so have the applications that rely on wireless networks.
• Wireless communication systems now include high-speed digital data networks capable of delivering voice, Internet, and even streaming video content to handheld units that users carry with them and use as they travel.
• Several systems have been proposed to satisfy the growing need for efficient, high-throughput packet data services.
• Wireless packet data systems have been designed to allow users to access packet data networks such as the Internet from stationary or mobile user equipment.
• the user equipment is sometimes called an Access Terminal (AT), which connects wirelessly with the Internet through a wireless infrastructure system called an Access Network (AN).
• AT Access Terminal
• AN wireless infrastructure system
• the AN generally includes multiple Access Points (AP), each having a limited transmit and receive range.
• AP Access Points
• the area within the transmit and receive range of a particular AP is a coverage area.
• a wireless data system that supports non-stationary ATs must permit an AT to move from the coverage area of one AP to that of another AP without losing the AT's connection with the AN.
• the process of rerouting data for an AT from a first AP to a second AP is called handoff. This rerouting process generally causes a brief interruption in data communication with the AT.
• a handoff of an AT from one AP to another AP may require changing channels within the same frequency band (intra- frequency handoff) or may require changing frequency bands (inter-frequency handoff).
• TIA-856-A The TIA-856-A standard, entitled “cdma2000 High Rate Packet Data Air Interface Specification,” and published by the Telecommunications Industry Association in 2004, describes methods of minimizing the duration of the interruption of data communication during intra-frequency handoff of an AT. But TIA-856-A does not provide ways to perform seamless inter-frequency handoff of an AT. Handoff of an AT from a source frequency band F 1 to a target frequency band F 2 will thus cause unacceptably long interruptions to services such as Voice over IP (VoIP), video telephony, network gaming, or other applications requiring high Quality of Service (QoS). Accordingly, it would be desirable to minimize the interruption in data flow that occurs during inter- frequency handoffs of an AT.
• VoIP Voice over IP
• QoS Quality of Service
• FIG. 1 is a high data rate system
• FIG. 2 is a call flow for intra-frequency handoff of an access terminal from a first sector to a second sector;
• FIG. 3 is a call flow for intra-frequency handoff of an access terminal from a first sector to a second sector using a DSC signal;
• FIG. 4 is a call flow for a handoff of an access terminal from a sector operating in a first frequency band to a sector operating in a second frequency band;
• FIG. 5 is a state diagram of operation of an access terminal throughout an inter- frequency handoff;
• FIG. 6 is a flowchart showing the steps in an illustrative inter-frequency handoff method; [0011] FIG.
• FIG. 7 is a block diagram of an illustrative access terminal apparatus configured to perform inter-frequency handoffs
• FIG. 8 is a block diagram of an illustrative access point apparatus configured to support inter-frequency handoff
• FIG. 9 is a block diagram of an illustrative access network controller.
• Embodiments disclosed herein address the above stated needs by providing an ability to perform handoff of an access terminal directly from a first sector operating in a first frequency band (transmitting and receiving on the forward and reverse links within an assigned frequency band or a pair of frequency bands) to a second sector operating in a second frequency band.
• a wireless communication system includes an access terminal configured to maintain an active set comprising at least one first frequency sector operating in a first frequency band and a pre-active set comprising at least one second frequency sector operating in a second frequency band that is different from the first frequency band, and to generate a data source control signal for transmission to an access network indicating a handoff to the at least one second frequency sector based on a signal parameter measurement associated with the at least one second frequency sector.
• the wireless communication system further includes the access network, which is configured to receive the data source control signal, to route user data addressed to the access terminal through the at least one first frequency sector before receiving the data source control signal, and to reconfigure a path of user data addressed to the access terminal from being sent through the at least one first frequency sector to being sent through the at least one second frequency sector after the expiration of a predetermined period after the data source control signal is received at the access network from the access terminal.
• the access network which is configured to receive the data source control signal, to route user data addressed to the access terminal through the at least one first frequency sector before receiving the data source control signal, and to reconfigure a path of user data addressed to the access terminal from being sent through the at least one first frequency sector to being sent through the at least one second frequency sector after the expiration of a predetermined period after the data source control signal is received at the access network from the access terminal.
• an access terminal apparatus includes a control processor configured to maintain an active set comprising at least one first frequency sector operating in a first frequency band and a pre-active set comprising at least one second frequency sector operating in a second frequency band that is different from the first frequency band, and to generate a data source control signal to be transmitted to an access network indicating a handoff to the least one second frequency sector based on a signal parameter measurement associated with the at least one second frequency sector.
• the access terminal apparatus further includes a signal measurement module configured to measure at least one parameter of transmissions received at the access terminal from the at least one second frequency sector, to provide the signal parameter measurement.
• an access network apparatus includes a router configured to route information between entities in the access network, wherein the router is configured to route user data addressed to an access terminal through a first access point associated with a first sector belonging to an active set corresponding to the access terminal, the active set comprising at least one first frequency sectors operating in a first frequency band.
• the access network apparatus further includes a control processor configured to perform, based on a data source control signal received from the access terminal, a router reconfiguration which causes the router to route user data addressed to the access terminal through a second access point associated with a second sector belonging to a pre-active set corresponding to the access terminal, the pre-active set comprising at least one second frequency sector operating in a frequency band that is different from the first frequency band.
• FIG. 1 shows a high data rate system (100) in accordance with an illustrative embodiment.
• an Access Terminal is defined broadly to include any stationary subscriber unit (108A or 108B) or mobile subscriber unit (106A, 106B, or 106C).
• An AT may communicate through a wireless channel or through a wired channel, for example using fiber optic or coaxial cables.
• An access terminal may further be any of a number of types of devices including but not limited to PC card, compact flash, external or internal modem, a desktop or laptop personal computer that includes an external or internal modem, or a wireless or wireline telephone.
• An AT typically provides a connection between a single user or computer and the wireless Access Network (AN). But a single AT may also provide a connection that may be shared by multiple concurrent users or computers.
• An AN generally includes multiple access points (e.g., wireless base stations), base station controllers, and/or switches connected to each other.
• An Access Point is defined broadly to include a single-sector or multiple- sector wireless base station, hub, or other network transceiver (104A-104G). Each AP has an associated coverage area called a "cell" (102A-102G), within which ATs may communicate with the AP at an acceptable data rate and signal quality level.
• an AP is part of the AN that provides a connection between one or more ATs and a terrestrial network such as the Internet. But an AP may also provide connections between one or more ATs and other types of networks, including other wireless networks.
• An AN may also provide a connection between one or more ATs and multiple networks, such as various combinations of corporate intranets, the Internet, and the Public Switched Telephone Network (PSTN).
• PSTN Public Switched Telephone Network
• the communication link through which an AT sends signals to access points in the AN is called a reverse link.
• the communication link through which APs send signals to an AT is called a forward link.
• the reverse link and forward link between an AP and an AT may reside within a single frequency band and be separated using time division duplexing. Alternatively, the reverse link and forward link between an AP and an AT may be separated by transmitting them within disjoint frequency bands.
• the term "frequency band" is used herein to mean either form of frequency assignment. In other words, an inter-frequency handoff between frequency bands in a system that uses time division duplexing to separate the forward link from the reverse link implies that an AT tunes its receiver and transmitter from one common frequency to a different common frequency.
• An inter-frequency handoff between frequency bands in a system that separates the forward and reverse links using disjoint frequency bands implies that an AT tunes its receiver and transmitter from one reverse-link/forward-link pair of frequencies to a different reverse-link/forward-link pair of frequencies.
• Wireless standards provide specifications that promote compatibility between various manufacturers of ATs and AN equipment.
• IxEV-DO also called 3GPP2 C.S0024-A or TIA-856- A
• an active AT has one or more sectors in its active set. Each sector in the active set is associated with a different pilot signal offset.
• An AP may have multiple sectors, making it possible for the active set to contain more than one sector for the same AP, or "cell.”
• the AT receives forward link data from one sector at a time.
• the AT sends a signal to the AN that indicates the best serving sector among the sectors in the active set. This signal is called the Data Rate Control (DRC) signal, and is generally transmitted on a DRC channel.
• DRC Data Rate Control
• the AT is said to "point" its DRC to the sector from which it may receive data next.
• the DRC signal also indicates to the AN the rate at which data should be sent to the AT.
• the AT generally varies the DRC signal based on measurements taken at the AT of one or more forward link signal parameters. For example, if an AP transmits a pilot signal, the AT may vary the DRC signal based on the measured strength of the pilot signal received from a selected AP. Where the AP has multiple sectors, the AT may also identify in the DRC signal a specific sector from which the AP may transmit data to the AT.
• FIG. 2 shows an illustrative call flow for an intra-frequency handoff of an AT from a sector of a first AP (AP 1 ) to a sector of a second AP (AP 2 ).
• the AN sends data (202) from AP 1 at the rate requested by the AT.
• the AT sends a DRC signal (204) requesting to switch the serving sector from a source sector in a first AP (AP 1 ) to a destination (target) sector in a second AP (AP 2 ).
• the AT may receive data (208) from the target sector of the second AP (AP 2 ).
• the AT may handoff between them without incurring the delay (206). But where the source and target sectors belong to different APs, the delay (206) is necessary to allow the AN to reroute data to the new cell. Even though the AT has pointed its DRC to a sector of the second AP (AP 2 ), the network will not be able to transport data to or from the AT through the second AP (APa) until after the delay (206). For some applications, this handoff process may result in an unacceptable interruption in the data flow.
• DSC Data Source Control
• This signal is sent from the AT to the AN, and indicates the cell to which the AT will point its DRC after a specified delay time.
• the specified delay time is measured in slots and is called "DSCLength.”
• DSCLength may be measured in some other time increment, or may be identified by some other technique such as by indicating an index into a lookup table of possible time periods.
• DSCLength is chosen to provide sufficient time for the AN to reroute forward link data from the source sector to the target sector identified in the DSC signal.
• the DSC signal provides advance notification to the AN of the AT' s intention to point its DRC at a sector belonging to the target cell, thereby minimizing the interruption in data flow to the AT caused by the handoff.
• FIG. 3 shows an illustrative call flow for intra-frequency handoff of an AT from a first AP (AP 1 ) to a second AP (AP 2 ) using a DSC signal.
• the AN sends data (310) from AP 1 at the rate requested by the AT.
• the AT sends a DSC signal (312) requesting to switch the serving sector from a source sector in a first AP (AP 1 ) to a target sector in a second AP (AP 2 ) after DSCLength slots.
• the AN provides the DSCLength parameter to the AT prior to the DSC signal (312).
• the AN may provide the DSCLength parameter in a traffic channel assignment message, in an overhead broadcast message, in a signaling message directed exclusively to the AT, or in some other message.
• the AT may use a default value for DSCLength that is not sent over any wireless channel.
• the AT may optionally send a DRC signal (314) requesting data from the source sector (AP 1 ).
• DSC signal (312) and DRC signal (314) are shown as transmitted from the AT only to the first AP (AP 1 ), any other AP operating in the same frequency band, including the second AP (AP 2 ), may also receive and decode signals transmitted by the AT.
• the AT directs its DRC signal (316) to the target sector to the target sector (AP 2 ).
• the AT may then receive data (318) from the target sector (AP 2 ).
• the AN may adjust DSCLength based on which sectors are in the active set of the AT. Based on this information, the AN may predict whether the AT will need to handoff to a target sector that is in the same cell as the source sector. If so, then the AN sets the DSCLength to a relatively short value. If the AT will likely handoff to a target sector in a different cell than the source sector, then the AN sets the DSCLength to a longer value to accommodate the longer time needed to reroute data through a different cell. By adjusting DSCLength based on this information, the AN may minimize or eliminate any interruption in the data flow caused by handoff.
• the AT is permitted to direct its DRC signals or its DSC signals at any sector that is in an "active set" assigned to the AT.
• the AN assigns to each AT an active set of one or more sectors using a TrafficChannelAssignment message.
• the AN also provides a "neighbor set” of sectors whose signals the AT may monitor for possible addition to the active set. For example, the AN may identify the "neighbor set” using a message such as a SectorParameters or NeighborList message as defined in TIA-856-A.
• the AT receives a strong signal from a sector in its neighbor set, it informs the AN by sending a RouteUpdate message.
• the AT may use the RouteUpdate message format specified in section 9.7.6.2.1 of TIA-856-A.
• the AN then sends a TrafficChannelAssignment message that removes the sector from the neighbor set and adds it to the active set.
• the AT informs the AN with a RouteUpdate message.
• the AN then sends a TrafficChannelAssignment message that removes the weak sector from the active set.
• the AT may not perform handoff. If the active set of an AT contains more than one sector, then the AT selects the sector in the active set based on the signal quality of the signals received by all sectors in the active set. The AT generally selects the sector from which it may receive data at the highest data rate. Once the AT identifies the best sector, it requests service from that sector using the DRC and DSC signals.
• the reverse link all sectors in the AT's active set simultaneously demodulate the signals transmitted by the AT. This allows the AT to establish reverse link channels to new sectors without tearing down existing ones. In contrast, before a new sector may transmit on the forward link to an AT, any existing forward link channels from other sectors must first be abandoned. Thus, the reverse link utilizes "soft handoffs," but the forward link utilizes only "hard handoffs.”
• the embodiments described above relate to intra-frequency handoff, i.e., wherein the source sector and the target sector transmit within the same frequency band. These handoff techniques do not work as well when the source sector and the target sector operate on different frequencies.
• the reverse link may not utilize soft handoff if the sectors in the active set are operating in different frequency bands. If two sectors transmit over different frequency bands, then they also receive data using different frequency bands.
• the AT generally operates in only one frequency band at a time. Therefore, all sectors in the AT's active set must transmit on the same frequency band and must receive on the same frequency band. In order for the AT to handoff to a sector on a new target frequency band, it must handoff to a sector that is not in its own active set. Also, upon performing such a handoff, all sectors operating in the old source frequency band must be immediately removed from the AT's active set.
• FIG. 4 shows an illustrative call flow for a handoff of an AT from a sector operating in a first frequency band (F 1 ) to a sector operating in a second frequency band (F 2 ) in accordance with an embodiment.
• the AT maintains an active set of sectors operating in the first frequency band (F 1 ) and a neighbor set of sectors.
• the neighbor set includes sectors operating in the first frequency band (F 1 ) and sectors operating in the second frequency band (F 2 ). While receiving data (410) from an F 1 sector, the AT occasionally tunes its receiver to F 2 to measure parameters of signals (412) received on F 2 .
• the AT sends a RouteUpdate message (414) indicating the strength of the F 2 signals.
• the AN sends a message (416) to the AT adding one or more sectors operating in F 2 to the pre-active set.
• the message (416) used to add sectors to the pre-active set identifies which sectors are in the pre-active set.
• the pre-active set sectors may be identified in a separate message such as an UpdateParameters message.
• the UpdateParameters message or a traffic channel assignment message indicates the DSC values associated with APs operating in frequencies in the pre-active set.
• the AT is allowed to point its DSC to a sector in the pre-active set (i.e., to a cell associated with a sector in the pre-active set).
• the AN may also send a message (418) to the AT indicating an InterfrequencyDSCLength value to be used in the event of a switch to a sector in the pre-active set.
• the AN optionally adjusts the DSCLength parameter used for handoff to any sector to be long enough to seamlessly switch to a sector in the pre-active set.
• the message (418) used to send the InterfrequencyDSCLength value may be an AttributeUpdateRequest, and may be sent in the same packet as message (416) or in a separate packet. Where a sector operating in the first frequency band (Fi) and the sector operating in a second frequency band (F 2 ) are collocated, the AN may set the DSCLength or InterfrequencyDSCLength to a relatively short value.
• the AT While receiving data from an F 1 sector, the AT occasionally retunes its receiver to F 2 to measure parameters of signals (420) received on F 2 from one or more sectors in the pre-active set. If the signals (420) from the one or more sectors in the pre-active set become sufficiently strong (for example, as compared to signals from sectors in the active set), the AT sends a DSC signal (422) indicating a switch to a target sector in the pre-active set. The AT will generally point its DSC to a sector on F 2 when the F 2 signals have become strong enough that it is desirable for the AT to start receiving data over F 2 . In an illustrative embodiment, the AT unilaterally changes its DSC without receiving any explicit direction or permission from the AN to do so.
• the AT may change its DSC to a sector on F 2 only after receiving a hard handoff direction message or a traffic channel assignment message from the AN that indicates an inter-frequency handoff.
• the AN uses pilot strength measurement information received from the AT to determine when to send the hard handoff direction message.
• the AT continues to direct DRC signals (424) to the selected sector operating in F 1 , and may receive data (426) from the selected F 1 sector.
• the AT tunes its receiver and transmitter to F 2 and may transmit DRC signals (428) indicating the data rate at which it may receive data (430) from the selected sector operating in F 2 .
• the AT and the AN switch the active and pre-active sets. In other words, the active set becomes the pre- active set, and at least one sector in the pre-active set becomes the new active set.
• the AT sends a RouteUpdate message indicating the measured received signal qualities of signals received from sectors in the pre-active set.
• the RouteUpdate message may be sent before, after, or at the same time as the DSC signal indicating a switch to a pre-active set sector.
• the AN may then send a TrafficChannelAssignment message that enables the AT to switch directly into soft handoff with more than one pre-active set sector.
• FIG. 5 is a state diagram showing the different states of the AT in an illustrative embodiment.
• the AT receives service (data) from an AP operating in F 1 .
• the AT maintains an active set of sectors operating in the first frequency band (F 1 ) and a neighbor set of sectors that may include sectors operating in the first frequency band (F 1 ) and sectors operating in a second frequency band (F 2 ).
• the AT occasionally tunes its receiver to F 2 to measure parameters of signals received on F 2 . If one or more of the F 2 signals becomes sufficiently strong (for example, as compared to signals from sectors in the active set), the AT sends a RouteUpdate message indicating the strength of the F 2 signals.
• the AN sends a message to the AT adding one or more sectors operating in F 2 to the pre-active set, at which time the AT transitions (512) to state (514).
• the AT may receive an InterfrequencyDSCLength value or a new DSCLength value to be used in the event of a switch to a sector in the pre-active set that causes it to transition (516) to state (518).
• the AT may receive data from active-set AP' s operating in F 1 , occasionally retuning its receiver to F 2 to measure parameters of signals received on F 2 from one or more sectors in the pre-active set.
• the AT transitions (526 or 532) to state (542), in which it sends a DSC signal indicating a switch to a target sector in the pre-active set.
• the AT transitions (540) to state (538), in which it transmits DRC signals to sectors in the active set operating in F 2 .
• the active set becomes the new pre-active set and the pre- active set becomes the new active set.
• the new active set consists of the entire group of sectors that previously made up the pre-active set
• the new pre-active set consists of the entire group of sectors that previously made up the active set.
• the new active set may instead consist of some subset of the group of sectors that previously made up the pre-active set, and/or the new pre-active set may instead consist of some subset of the group of sectors that previously made up the active set.
• the AT instead transitions (524) to state (522), in which it directs its DSC signal to the strongest AP operating in F 1 .
• the AT could then transition (520) to state (514), and direct its DRC signals to and receive data from an F 1 sector.
• the AT could theoretically transition (530 and 524) back and forth between state (522) and state (542) indefinitely without receiving data.
• the AT once the AT transitions to a state (542) in which it switches from one frequency band to another, it must automatically transition (540) to a state (538) in which it may receive data at the new frequency band for at least a minimum time period, for example DSCLength. This minimum time period prevents the "ping-ponging" effect that could otherwise occur without any data being received at the AT.
• the AT While the AT is in state (538), it may receive data from active-set AP' s operating in F 2 , occasionally retuning its receiver to F 1 to measure parameters of signals received on F 1 from one or more sectors in its pre-active set. If the signals from at least one sector in the F 1 pre-active set become sufficiently strong (for example, exceeding the signal strength of the strongest sector in the active set by a predetermined amount), the AT transitions (528) to state (522), in which it sends a DSC signal indicating a switch to a target sector in the pre-active set.
• the AT transitions (536) to a state (534) in which the "weak" F 1 sector is removed from the pre-active set.
• the AT removes an F 1 sector by sending a RouteUpdate message indicating the sector's weak received signal.
• the AN then sends the AT a TrafficChannelAssignment or other message directing the AT to remove the F 1 sector from the pre-active set.
• the AT continues to direct DRC signals (424) to the selected sector operating in
• the AT tunes its receiver and transmitter to F 2 and may transmit DRC signals (428) indicating the data rate at which it may receive data (430) from the selected sector operating in F 2 .
• the active set becomes the pre-active set, and at least one sector in the pre-active set is included within the new active set.
• the AT sends a RouteUpdate message indicating the measured received signal qualities of signals received from sectors in the pre-active set.
• the RouteUpdate message may be sent before, after, or at the same time as the DSC signal indicating a switch to a pre-active set sector.
• the AN may then send a TrafficChannelAssignment message that enables the AT to switch directly into soft handoff with more than one pre-active set sector.
• FIG. 6 is a flowchart showing the steps in an illustrative embodiment of an inter- frequency handoff method.
• the AT may receive data from active-set sector AP 1 operating in frequency band F 1 .
• the AT periodically measures a parameter, such as pilot strength, of a signal received from pre-active-set sector AP 2 operating in frequency band F 2 . If the measured F 2 parameter indicates that the AT could receive data from sector AP 2 , then AP 2 is added to the pre-active set of the AT at step (614). Otherwise, if the AP 2 received signal is too weak to justify adding AP 2 to the pre-active set, then the AT continues at step (610) to receive data from sector AP 1 .
• a parameter such as pilot strength
• the AT may receive data from sector AP 1 at step (616). While receiving data from sector AP 1 , the AT periodically tunes its receiver to F 2 at step (618) and measures receiver parameters for signals received from sector AP 2 . If the signals received from sector AP 2 become strong enough to warrant switching to F 2 , then at step (620) the AT hands off to AP 2 operating in F 2 . Conversely, if the signals received from sector AP 2 are not strong enough to warrant switching to F 2 , then step (616) is repeated and the AT may continue to receive data from sector AP 1 .
• the AT may receive data from sector AP 2 at step (624). While receiving data from sector AP 2 , the AT periodically tunes its receiver to F 1 at step (626) and measures receiver parameters for signals received from sector AP 1 . If the signals received from sector AP 1 become strong enough to warrant switching back to F 1 , then at step (622) the AT hands off to AP 1 operating in F 1 . Conversely, if the signals received from sector AP 1 are not strong enough to warrant switching back to F 1 , then step (624) is repeated and the AT may continue to receive data from sector AP 2 .
• FIG. 7 is a block diagram of an AT apparatus in accordance with an illustrative embodiment.
• Data is encoded and interleaved in Encoder/Interleaver (712).
• This data includes user data such as voice data, streaming video, or web browser data. This data also includes call control messages used for setup, tear-down, and handoffs of the communication link between the AT and the AN.
• Encoder/Interleaver (712) may use any of a variety of encoding techniques including forward error correction codes, syndrome codes, convolutional codes, and turbo codes.
• Encoder/Interleaver (712) may also use any of a variety of interleaving techniques such as block interleaving or bit- reversal interleaving.
• Encoder/Interleaver (712) also performs signal-point conversion of the binary data into a form more suitable to spreading using Walsh and PN codes.
• the Encoder/Interleaver (712) encodes and interleaves the data to provide encoded data.
• the encoded data is then multiplied by a channel code such as a Walsh code in Walsh Spreader (714).
• a channel code such as a Walsh code in Walsh Spreader (714).
• PN Pseudorandom Noise
• the Walsh Spreader (714) channel codes the encoded data to provide channel coded data.
• the channel coded data is then spread by multiplying it by a complex PN code in PN spreader (716).
• PN spreader 716
• the despreader could alternatively utilize Gold codes or simple (real) PN codes.
• the channel coded data is PN spread in PN Spreader (716) to provide PN spread data.
• the PN spread data is then upconverted to radio frequencies and amplified in Upconverter/ Amplifier (718).
• Upconverter/Amplifier (718) also modulates the PN spread data using any of a variety of modulation techniques such as BPSK, QPSK, 16-QAM or 256-QAM.
• Upcon verier/ Amplifier (718) receives a frequency control signal from Control Processor (720) that controls the transmit frequency of the AT.
• the Upcon verier/ Amplifier (718) generates amplified data from the PN spread data.
• the amplified data is then provided to a diplexer
• Diplexer (722) also permits signals received through antenna (724) to be provided to a Downconverter/ Automatic Gain Control (AGC) (758) with minimal feedback interference from the amplified data generated by Upconverter/ Amplifier (718).
• AGC Automatic Gain Control
• Downconverter/ AGC (758) downconverts signals received at the AT from the
• Downconverter/AGC also performs an AGC (automatic gain control) function to minimize quantization noise inserted into the data stream during the analog-to-digital conversion process.
• AGC automatic gain control
• the extent of AGC needed is also used as a measure of overall received signal strength at the receiver frequency. This AGC information is provided to Control Processor (720).
• the do wncon verted signal generated at Downconverter/AGC (758) is PN despread by multiplying the downconverted signal by a complex PN code at PN despreader (756), similar to the PN Spreader (716), multiplying it by a complex PN code in PN spreader (716).
• PN despreader 756 could alternatively utilize Gold codes or simple (real) PN codes.
• the signals transmitted from APs in the AN include a pilot channel signal that is either unmodulated with a Walsh code or utilizes the all-ones Walsh code.
• the raw output of the PN despreader (756) is provided to a Pilot Measurement Module (726) which measures the strength of the pilot signal received from each sector.
• Pilot Measurement Module (726) could perform a simple integrate and dump function to provide a measure of energy-per-chip over noise-and-interference (E c /N 0 ) of the received pilot signal.
• the Pilot Measurement Module (726) is implemented as a circuit of an Application-Specific Integrated Circuit (ASIC).
• ASIC Application-Specific Integrated Circuit
• the Pilot Measurement Module (726) and the Control Processor (720) may reside within a common device such as an ASIC, or may reside within separate devices.
• the Pilot Measurement Module (726) may include an integrate-and-dump circuit.
• the Pilot Measurement Module (726) generates a pilot measurement signal that is provided to the Control Processor (720).
• the Pilot Measurement Module (726) may measure some alternate parameter of the received signals other than strengths of pilot signals. For example, the Pilot Measurement Module (726) could instead estimate E c /No of a channel other than a pilot channel, such as a broadcast channel that carries data. In such an alternate embodiment, the Pilot Measurement Module (726) generates a signal strength measurement based on the alternate parameter and provides that information to the Control Processor (720).
• the output of PN Despreader (756) is also provided to Walsh Despreader (754) which multiplies the PN-despread signal by one or more channel codes to extract the different channel signals.
• the PN-despread signal is multiplied by one or more Walsh symbols, and integrated over a Walsh symbol period to determine the symbol value for each Walsh symbol.
• Walsh Spreader (714) one of skill in the art will recognize another type of despreader using an alternate type of channel code could be used without departing from the illustrative embodiment.
• an alternate channel decoder may employ Gold codes, PN codes, or other orthogonal or non-orthogonal codes.
• Decoder/Deinterleaver (752) are decoded and deinterleaved in Decoder/Deinterleaver (752).
• Decoder/Deinterleaver (752) may use any of a variety of decoding techniques such as trellis decoding for convolutional codes, block codes, syndrome codes, and turbo codes.
• Decoder/Deinterleaver (752) may also use any of a variety of interleaving techniques such as block deinterleaving or bit-reversal deinterleaving.
• Decoder/Deinterleaver (752) also converts the decoded and deinterleaved signal into binary data. The resultant binary data stream is then provided to Control Processor (720).
• call control messages to be encoded and interleaved in Encoder/Interleaver (712) are generated by a control processor (720).
• Control processor (720) may be any of a variety of devices capable of performing the functions described herein, such as a general purpose processor, a digital signal processor (DSP), or an application specific integrated circuit (ASIC).
• Control processor (720) may include memory (not shown) for storing program instructions and temporary data. This memory may include, for example, flash memory, Electrically Erasable Programmable Read-Only Memory (EEPROM), Random Access Memory (RAM), or any other type of memory suitable for storing program instructions and data needed to perform the functions described herein.
• EEPROM Electrically Erasable Programmable Read-Only Memory
• RAM Random Access Memory
• the functions of the Control Processor (720) include receiving the decoded messages such as TrafficChannelAssignment and AttributeUpdateRequest messages through Decoder/Deinterleaver (752) and specifying DSC signals, DRC signals, and RouteUpdate messages that are transmitted through Encoder/Interleaver (712). Additionally, the Control Processor (720) controls the upconversion and downconversion frequencies utilized by the Upconverter/ Amplifier (718) and Downconverter/AGC (758), respectively, during inter-frequency handoffs.
• decoded messages such as TrafficChannelAssignment and AttributeUpdateRequest messages through Decoder/Deinterleaver (752) and specifying DSC signals, DRC signals, and RouteUpdate messages that are transmitted through Encoder/Interleaver (712). Additionally, the Control Processor (720) controls the upconversion and downconversion frequencies utilized by the Upconverter/ Amplifier (718) and Downconverter/AGC (758), respectively, during inter-frequency handoffs
• FIG. 8 is a block diagram of an AP apparatus (104) in accordance with an illustrative embodiment.
• the AN typically includes multiple APs and may also include a central controller (not shown) that routes data between the various other components of the AN, including each AP.
• Data is encoded and interleaved in Encoder/Interleaver (812).
• This data includes user data such as voice data, streaming video, or web browser data.
• This data also includes call control messages used for setup, tear-down, and handoffs of the communication link between the AT and the AN.
• Encoder/Interleaver (812) may use any of a variety of encoding techniques including forward error correction codes, syndrome codes, convolutional codes, and turbo codes.
• Encoder/Interleaver (812) may also use any of a variety of interleaving techniques such as block interleaving or bit-reversal interleaving. In an illustrative embodiment, Encoder/Interleaver (812) also performs signal-point conversion of the binary data into a form more suitable to spreading using Walsh and PN codes. The Encoder/Interleaver (812) encodes and interleaves the data to provide encoded data.
• the encoded data is then multiplied by a channel code such as a Walsh code in Walsh Spreader (814).
• a channel code such as a Walsh code in Walsh Spreader (814).
• a channel code such as a Walsh code in Walsh Spreader (814).
• Walsh Spreader 814
• an alternate channel coder may employ Gold codes, PN codes, or other orthogonal or non- orthogonal codes.
• the Walsh Spreader (814) channel codes the encoded data to provide channel-coded data.
• the channel coded data is then spread by multiplying it by a complex PN code in PN spreader (816).
• the despreader could alternatively utilize Gold codes or simple (real) PN codes.
• the channel-coded data is PN spread in PN Spreader (816) to provide PN spread data.
• the PN spreader (816) may further be configured to inject a pilot channel signal into the PN-spread data.
• the PN spreader (816) might add a gain-adjusted all-ones Walsh signal to the output of the Walsh spreader before providing its output signal to Upconverter/Amplifier (818).
• the PN spread data is then upconverted to radio frequencies and amplified in Upconverter/Amplifier (818).
• Upconverter/Amplifier (818) also modulates the PN spread data using any of a variety of modulation techniques such as BPSK, QPSK, 16-QAM or 256-QAM.
• Upconverter/Amplifier (818) receives a frequency control signal from Control Processor (820) that controls the transmit frequency of the AT.
• the Upconverter/Amplifier (818) generates amplified data from the PN spread data.
• the amplified data is then provided to a diplexer
• Diplexer (824) also permits signals received through antenna (824) to be provided to a Downconverter/AGC (858) with minimal feedback interference from the amplified data generated by Upconverter/Amplifier (818).
• Downconverter/AGC (858) downcon verts signals received at the AT from the
• Downconverter/AGC (858) also performs an AGC (automatic gain control) function to minimize quantization noise inserted into the data stream during the analog-to-digital conversion process.
• AGC automatic gain control
• the extent of AGC needed is also used as a measure of overall received signal strength at the receiver frequency. This AGC information is provided to Control Processor (820).
• the downconverted signal generated at Downconverter/AGC (858) is PN despread by multiplying the downconverted signal by a complex PN code at PN despreader (856). Similar to PN Spreader (816) multiplying it by a complex PN code in PN spreader (816).
• PN despreader could alternatively utilize Gold codes or simple (real) pseudo-noise (PN) codes.
• the output of PN Despreader (856) is also provided to Walsh Despreader (854) which multiplies the PN-despread signal by one or more channel codes to extract the different channel signals.
• the PN-despread signal is multiplied by one or more Walsh symbols, and integrated over a Walsh symbol period to determine the symbol value for each Walsh symbol.
• Walsh Spreader (814) one of skill in the art will recognize that another type of despreader that uses an alternate type of channel code could be used without departing from the illustrative embodiment.
• an alternate channel decoder may employ Gold codes, pseudo-noise (PN) codes, or other orthogonal or non-orthogonal codes.
• Decoder/Deinterleaver (852) are decoded and deinterleaved in Decoder/Deinterleaver (852).
• Decoder/Deinterleaver (852) may use any of a variety of decoding techniques such as trellis decoding for convolutional codes, block codes, syndrome codes, and turbo codes.
• Decoder/Deinterleaver (852) may also use any of a variety of interleaving techniques such as block deinterleaving or bit-reversal deinterleaving.
• Decoder/Deinterleaver (852) also converts the decoded and deinterleaved signal into binary data. The resultant binary data stream is then provided to Control Processor (820).
• call control messages to be encoded and interleaved in Encoder/Interleaver are generated by a control processor (820).
• Control processor (820) may be any of a variety of devices capable of performing the functions described herein, such as a general purpose processor, a digital signal processor (DSP), or an application specific integrated circuit (ASIC).
• Control processor (820) may include memory (not shown) for storing program instructions and temporary data. This memory may include, for example, flash memory, electronically-erasable programmable read-only memory (EEPROM), random access memory (RAM), or any other type of memory suitable for storing program instructions and data needed to perform the functions described herein.
• the functions of the Control Processor (820) include receiving and interpreting DSC signals, DRC signals, and RouteUpdate messages that are received through Decoder/Deinterleaver (852), and forming messages such as TrafficChannelAssignment and AttributeUpdateRequest messages to be provided to Encoder/Interleaver (812) for transmission to ATs.
• the Control Processor (820) also coordinates the transmission of neighbor sets and identifies the operating frequencies of other APs in the AN.
• the Control Processor (820) sends and receives information to other entities in the AN through a backhaul interface (828) to a backhaul connection (826).
• the AP when the AP receives a DSC signal from an AT indicating that the AT will handoff to a frequency band other than the frequency band on which the AP is transmitting, the AP forwards the information to one or more other entities in the AN through the backhaul connection (826). The AP then participates in the synchronized switching of routing of data to the AT.
• the AN includes at least one Access Network
• FIG. 9 is a block diagram of an illustrative embodiment of an ANC.
• the ANC communicates with the other entities in the AN through its own backhaul interface (914).
• the ANC receives user data addressed to the AT from an external network such as the Internet and routes this user data through a router (918) to the corresponding serving AP for transmission to the AT over the forward link.
• data received from each AT addressed to an entity in the external network is routed through the router (918) of the ANC.
• a Control Processor (910) within the ANC receives DSC information from all
• the Control Processor (910) may receive the DSC information through a connection (912) with the backhaul interface (914). Alternatively, the Control Processor (910) may transmit and receive information from APs in the AN through the Router (918), in which case the data connection (912) between the Control Processor (910) and the backhaul interface (914) may be unnecessary.
• the ANC coordinates the timing of rerouting of user data necessitated by handoffs of an AT from one AP to another. Based on received DSC information, the Control Processor (910) adjusts the path of user data through the router (918).
• the ANC when the ANC receives DSC information indicating an inter-frequency hard handoff of an AT from a serving sector to a target sector, the ANC reconfigures the router (918) so that data addressed to the AT is routed to the target sector at the appropriate time.
• the APs coordinate hard handoff rerouting among them without the ANC reconfiguring the router (918).
• the serving AP remains in the active set of the AT and continues to send and receive data from the AT until the expiration of the appropriate delay period (DSCLength or InterfrequencyDSCLength). After the expiration of the appropriate delay period, the serving AP is moved from the active set of the AT to the pre-active set of the AT, and no longer sends data to, or receives data from, the AT.
• each of the embodiments illustrated in FIGs. 7-9 may include a memory storage unit, such as a Look up Table, (not shown) for storing active set and/or pre- active set information. Additionally, such memory storage may also store parameters used in handoff decisions.
• a memory storage unit such as a Look up Table, (not shown) for storing active set and/or pre- active set information. Additionally, such memory storage may also store parameters used in handoff decisions.
• DSP digital signal processor
• ASIC application specific integrated circuit
• FPGA field programmable gate array
• a general purpose processor may be a microprocessor, but in the alternative, the processor may be any conventional processor, controller, microcontroller, or state machine.
• a processor may also be implemented as a combination of computing devices, e.g., a combination of a DSP and a microprocessor, a plurality of microprocessors, one or more microprocessors in conjunction with a DSP core, or any other such configuration.
• a software module may reside in RAM memory, flash memory, ROM memory, EPROM memory, EEPROM memory, registers, hard disk, a removable disk, a CD-ROM, or any other form of storage medium known in the art.
• An illustrative storage medium is coupled to the processor such the processor may read information from, and write information to, the storage medium.
• the storage medium may be integral to the processor.
• the processor and the storage medium may reside in a single ASIC.
• the ASIC may reside in an access terminal or in an access point.
• the processor and the storage medium may reside as discrete components in a user terminal.

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